For the spring semester, my colleague Dave Rogers and I are teaching a seminar class entitled “Human Phylogeography.” Phylogeography is the study of the history of the genetic variation, and of genetic lineages, within a species (or closely related group of species), and in the seminar we are looking at the phylogeography of human populations. DNA sequencing now allows a fine scale mapping of the distribution of genetic variation within and among populations, and, remarkably, the ability to sequence ancient DNA from fossil remains (including Neanderthals). The seminar is based primarily on a close reading of David Reich’s (2018) Who We Are and How We Got Here (published by OUP in the UK).
Although rarely under that rubric, human phylogeography has been a frequent topic of discussion here at WEIT, by Jerry, Matthew, and myself, including our several discussions of Neanderthals (or Neandertals) and Denisovans. So it may be of interest for WEIT readers to follow along. Below the fold I’ve placed the course syllabus, which includes the readings, and links to many newspaper articles of interest, and online postings, including many here at WEIT, and also from John Hawks Weblog, a site we’ve recommended on a number of occasions when discussing human evolution. (The newspaper links appear as images; just click to go to the story.) We just finished our third meeting, and I’ve been quite impressed by the students’ discussion and writing. We’re fortunate to have some students from anthropology or with some anthro background.
Please read along with us, or browse what seems interesting below. If you have questions or comments, post them here, and I’ll be looking in.
This week’s Science magazine has an absorbing article by Sarah Tishkoff et al. on the genetic relationship and evolutionary history of African populations. (Ann Gibbons has a one-page summary here.) This project was a massive one, involving DNA genotyping of 1,327 genes in 2,432 Africans from 113 populations, as well as 98 African-Americans and 21 Yemenites. (That’s over 3,385,000 genetic determinations; no wonder the paper has 25 authors!) There are many results, but I’ll just list the main ones here:
1. All the hunter-gatherer populations of Africa descend from one ancestral population that is a bit more than 35,000 years old. This means that African tribes and ethnic groups are very young relative to when African ancestors left the continent to populate the world with modern humans (about 60,000-100,000 years ago).
2. The population ancestral to the modern African groups appears to have lived in southwest Africa. Tishkoff et al. even calculate a migration epicenter: 12.5 degrees E and 17.5 degrees S, near the border of Namibia and Angola.
3. The genetic profile of Africans put them roughly into groups corresponding to the major language differences (see figure below). This is not surprising; it shows that almost all intermarriage has occurred within groups that speak the same language.
4. African-Americans have a complex mixture of genes from many areas, including about 67% Bantu and non-Bantu genes from people who speak Niger-Kordofanian languages (e.g. ,Zulu and Swahili), 8% from other African areas, and 13% from Caucasians. The authors note that this will make it hard for some African-Americans to trace their roots.
5. The “out of Africa” group whose migration gave rise to modern humans worldwide has its closest relatives in the group of “blue” populations at the top of the figure below. These are “Saharan” populations from East Africa. That, then, is where the rest of us came from.
The phylogeny of African groups: a massive achievement (Figure from Tishkoff et al.)